In my opinion the recommendation that weightlifters eat 1-1.5gPRO/lb/d, which is 2.2x more protein than required, comes from the supplements industry who rely on people used to thinking in pounds not calculating their protein requirements correctly to sell product.

An athlete weighing a convenient 100kg (220 lbs) for example would have a protein intake of 100-140g/d, which is an amount that can easily be obtained by diet alone, if they based their intake on the correct 1-1.4g/kg/d. That same athlete eating 1-1.5g/lb/d would have a protein intake of 220-330g/d which would be impractical to obtain through diet alone unless they were willing to eat a whole chicken or two per day. Supplements therefore become the only practical way for that athlete to achieve a protein intake of 1-1.5g/lb/d on a daily basis so the supplements industry clearly benefits from people getting mixed up over whether protein intakes should be based on g/lb or g/kg.

Finally, I'm well aware of anecdotal evidence from weightlifters and bodybuilders who claim that eating large amounts of protein and using supplements lead to increased strength and size but protein in excess of 1.8-2g/kg/d is oxidized to provide energy so all those protein supplements are doing really is providing the extra calories required for growth.